1. Field of the Invention
The present invention relates to an illuminating optical system for use in a projecting exposure device.
2. Related Art Statement
According to improvements of integration in recent semiconductor device, devices, the resolving power required in a projecting exposure device becomes higher from year to year. In order to improve the resolving power, various methods such as an effect of making the wavelength of the light source short, adoption of a phase shift method, an adoption of a versional illuminating method or the like have been studied and developed. Particularly, the versional illuminating method has an advantage that it does not require a large modification for the conventional device.
As a typical example of the versional illuminating method, there are (1) a method referred to as four pole illumination or four point illumination, by which the passing position of the light flux passing through the aperture diaphragm of the illuminating optical system is limited at four positions separated from the optical axis, and (2) a method referred to as a zonal illumination in which the passing position of the light flux passing through the aperture diaphragm of the illuminating optical system is limited in the zonal shape concentrical to the optical axis. It is particularly well known that four pole illumination has remarkable effects of improving resolving power and increasing focal depth for the pattern of lines in length and width. Zonal illumination has effects of improving resolving power and increasing focal depth for the pattern of lines in length and width, which are not remarkable for four pole illumination, but have a characteristic that no dependency for the direction of the reticle is present.
A conventional example of the four pole illumination is shown, for example, in FIGS. 42 and 43. In the example shown in FIG. 42, the illuminating light flux from a light source section comprising an ellipsoidal mirror 102, a mercury lamp 103 and a lens 104 is incident on a fly-eye lens 108 and divided or separated into four by an aperture diaphragm 109a having four circular apertures, which directly follows the fly-eye lens.
In the example shown in FIG. 43, as is disclosed in Japanese Patent Application Opened No. 225,357/92, the illuminating light flux from a light source section comprising an ellipsoidal mirror 102, a mercury lamp 103 and a lens 104 is divided or separated into four by an optical fiber 121 which is branched into four.
A conventional example of the zonal illumination is shown, for example, in FIGS. 44 and 45. In the example shown in FIG. 44, the illuminating light flux from a light source section comprising an ellipsoidal mirror 102, a mercury lamp 103 and a lens 104 is incident on a fly-eye lens 108 and limited zonally by an aperture diaphragm 109b having zonal apertures, which is provided directly after the fly-eye lens.
In the example shown in FIG. 45, the illuminating light flux from a light source section comprising an ellipsoidal mirror 102, a mercury lamp 103 and a lens 104 is zonally converted by an axicon lens 122, which is provided directly after the lens 104.
In the above respective conventional examples, the four separated illuminating light flux, or the zonally converted illuminating light flux reaches a wafer 113 through a condenser lens 110, a reticle 111 and an imaging optical system 112.
In the above conventional example shown in FIG. 42, only the illuminating light flux which reaches the aperture provided to the aperture diaphragm 109a can be transmitted through the aperture, so that the utilization efficiency of the light flux of the light from the light source is decreased remarkably, thereby causing remarkable illuminance unevenness. In the above conventional example shown in FIG. 43, the utilization efficiency of the light flux of the light from the light source can be increased, but a number of optical fibers are necessary, so that the construction thereof becomes complicated and thus manufacture thereof becomes difficulty, resulting in a decrease in mechanical reliability. In the above conventional example shown in FIG. 44, only the illuminating light flux which reaches the aperture provided to the aperture diaphragm 109a can be transmitted through the aperture, so that the utilization efficiency of the light flux of the light from the light source is decreased remarkably. In the above conventional example shown in FIG. 45, the utilization efficiency of the light flux of the light from the light source can be increased, but the device becomes expensive, since it is necessary to use the axicon lens which is difficult to manufacture.